Surface position measuring method and apparatus

ABSTRACT

A measuring apparatus for measuring a position of a surface of an object while the object is scanned in a scanning direction in an X-Y plane. A detecting unit detects the position of the surface of the object in a Z direction perpendicular to the X-Y plane, a stage scans the object relative to the detecting unit in the scanning direction, and a controller causes the stage to pre-scan the object relative to the detecting unit in two scanning directions, in the X-Y plane, opposite to each other, to detect, using the detecting unit, with respect to each of the two scanning directions, a position of the surface in the Z-direction for each of the same detection points on the surface, to determine, with respect to each of the two scanning directions, a reference surface based on the detected positions of the surface, to calculate an offset value, which is a difference between the detected position and a position of the reference surface in the Z-direction for each of the same detection points with respect to each of the two scanning directions, to calculate a correction value for correcting the calculated offset value in accordance with a corresponding one of the two scanning directions based on a difference, in the Z-direction, between positions of the determined reference surfaces obtained with respect to the two scanning directions.

This application is a divisional application of U.S. patent applicationSer. No. 10/777,192, filed Feb. 13, 2004, which was published as U.S.Patent Application Publication No. 2005/0169515 A1 on Aug. 4, 2005.

This application also claims priority from Japanese Patent ApplicationNo. 2003-035170, filed on Feb. 13, 2003, which is hereby incorporated byreference herein.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to surface position detecting technology fordetecting a position of a surface of an object, particularly, for use inan exposure apparatus of a slit scan type (scanning exposure method).

The size of circuit patterns has been reduced to meet enlargement ofintegration of VLSI, and projection lens systems currently used inprojection exposure apparatuses have an enlarged numerical aperture(NA). Also, the allowable depth of focus of lens systems used in atransfer process of the circuit pattern has been narrowed. Thus, inorder to ensure superior pattern transfer, a process region (shot) to beexposed of a wafer as a whole should be exactly positioned within thedepth of focus of the projection lens system.

In slit-scan type exposure apparatuses, in order to assure good patterntransfer over the whole process region to be exposed, the position andtilt of the wafer surface (subject to be exposed) is detected preciselyduring scan motion. During the scan exposure, corrective drive ofauto-focusing and auto-leveling is carried out continuously to therebysuccessively bring the wafer surface into registration with a bestimaging plane of the projection optical system.

Surface position detecting mechanisms therefor include one in which alight beam is projected onto a wafer surface in an oblique direction andreflection light from the wafer surface is detected as a positionaldeviation upon a sensor, and one in which a gap sensor, such as an airmicrosensor or electrostatic capacitance sensor, is used. Anyway, inthese types, during the scan, from a plurality of level measured values,a corrective driving amount for the level and tilt of the wafer surface,when the same passes through the exposure slit region, is calculated.

Further, in the detecting mechanism described above, in order to assurethat a process region (shot) of a wafer as a whole is exactly positionedwithin the allowable depth of focus of a reduction projection lenssystem, having been narrowed with the enlargement of the NA, detectionpoints are set at plural locations inside each shot region of the wafer,and differences between detected values and a best focus setting planeare stored as measurement offset and are controlled exactly, this beingmade to avoid erroneous detection of a wafer surface (focus settingplane) due to the influence of any local pattern step (topography) undera detection point (or reflection point).

FIG. 4 schematically illustrates an alternating scan for process regionson a wafer. In this example, there are six sample shots with respect toeach of which pre-scanning in up and down directions are carried out,whereby a corrective drive amount toward a best imaging position iscalculated.

With decreasing size of circuit patterns, the NA of reduction projectionsystems has been enlarged and, on the other hand, the allowable depth offocus in a transfer process of the circuit pattern has been narrowed.Currently, in exposure apparatuses used for a rough pattern process, theallowable depth of focus is 1 μm or more, such that a measurement errorincluded in measured values obtained successively during the scanexposure or influences of a surface step (difference in level) withinthe chip can be disregarded. However, in order to meet 1 GDRAM, thedepth will be not greater than 0.3 μm. Thus, a measurement errorincluded in the measured values or the influence of a surface step inthe chip will not be disregarded.

Thus, when the focus of the wafer surface (level and tilt) is measured,and then focusing is carried out to hold the wafer surface within theallowable depth, since the wafer surface has surface irregularities, inorder to assure that the entirety of the chip or shot is registered withthe imaging plane, it is necessary to perform offset correction, whileexactly reflecting offsets memorized beforehand. Otherwise, theallowable depth cannot be held. In this case, accurate offset correctionis unattainable, unless the focus measurement point during exposure ofeach shot is exactly registered with the offset measurement point.

In the slit scan exposure method, the time for moving back the reticlestage is useless. Therefore, generally, alternate scan is adopted,taking into account the throughput. However, in a conventional surfaceposition detecting method, no particular attention has been paid to thefact that the measurement position (region of the subject ofmeasurement) shifts between the up and down scan directions, and a focuscorrection amount toward the best imaging plane position is calculatedand controlled, while taking the central position of the shot, forexample, as a reference (offset reference surface). If, therefore, thewafer surface position corresponding to the measurement point taken as areference differs with the scan direction, as shown in portions (i) and(ii) in FIG. 6, there would occur a difference in the focus correctingamount toward the best imaging plane position, between the up and downdirections, as shown in a portion (iii) of FIG. 6. An undesirabledefocus will be produced due to this difference with the direction.

Factors for such positional deviation may be as follows. A wafer stagecontrol system drives a wafer with a control cycle of the wafer stagecontrol system, on the basis of the stage position, as measured atpredetermined sampling intervals. If the control cycle of the waferstage control system is T_(s) and the moving speed of the wafer stage isV_(s), the measurement position will be dispersed by T_(s)×V_(s), at thelargest. This is called “jitter”. FIG. 5 illustrates an example of it.At the start position of a shot, the sample clock is reset. Aftersynchronism with the start position is taken, scan in a direction of anarrow is initiated. When each measurement point is detected at thetrailing edge of the clock, there is a positional deviation produced sothat a point 502 is detected, despite that a point 501 should bedetected.

Such jitter is changeable with the stage speed. Particularly, the stagespeed is recently increasing for improvement of the throughput.Therefore, the influence of a deviation of measurement positionresulting from jitter upon the focus precision cannot be disregarded.Such inconveniences might be solved by using high-speed control hardwareto shorten the control intervals, thereby to reduce the jitter close tozero, in order to decrease the difference between the up and down scandirections. With this method, however, not only will the cost rise, butalso, the structure is exclusively arranged for the difference betweenscan directions, such that the whole system lacks a good balance.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide asurface position detecting technology by which the position of a surfaceof an object can be detected very precisely.

In accordance with one aspect of the present invention, a methodincludes a detecting step of pre-scanning an object relative to adetection unit in two scanning directions, in an X-Y plane, opposite toeach other, the detection unit being configured to detect a position ofthe surface of the object in a Z direction perpendicular to the X-Yplane, and detecting, using the detection unit, with respect to each ofthe two scanning directions, a position of the surface in theZ-direction for each of the same detection points on the surface, acalculating step of determining, with respect to each of the twoscanning directions, a reference surface based on the detected positionsof the surface obtained in the detecting step, calculating an offsetvalue, which is a difference between the detected position and aposition of the reference surface in the Z-direction for each of thesame detection points with respect to each of the two scanningdirections, calculating a correction value for correcting the calculatedoffset value in accordance with a corresponding one of the two scanningdirections based on a difference, in the Z-direction, between positionsof the determined reference surfaces obtained with respect to the twoscanning directions, a correcting step of correcting, to obtain themeasured position, the position of the surface detected by the detectionunit while the object is scanned relative to the detection unit in oneof the two scanning directions, in accordance with a corresponding oneof the two scanning directions, with the calculated offset value and thecalculated correction value obtained in the calculating step, a scanningstep of scanning the object in one of the two scanning directions, amoving step of moving the scanning object in the Z direction based onthe corrected position obtained in accordance with a corresponding oneof the two scanning directions in the correcting step, and an exposingstep of exposing the scanning, moving object to a pattern.

In accordance with another aspect of the present invention, a measuringapparatus, for measuring a position of a surface of an object while theobject is scanned in a scanning direction in an X-Y plane, includes adetecting unit configured to detect the position of the surface of theobject in a Z direction perpendicular to the X-Y plane, a stageconfigured to scan the object relative to the detecting unit in thescanning direction, and a controller configured to cause the stage topre-scan the object relative to the detecting unit in two scanningdirections, in the X-Y plane, opposite to each other, to detect, usingthe detecting unit, with respect to each of the two scanning directions,a position of the surface in the Z-direction for each of the samedetection points on the surface, to determine, with respect to each ofthe two scanning directions, a reference surface based on the detectedpositions of the surface, to calculate an offset value, which is adifference between the detected position and a position of the referencesurface in the Z-direction for each of the same detection points withrespect to each of the two scanning directions, to calculate acorrection value for correcting the calculated offset value inaccordance with a corresponding one of the two scanning directions basedon a difference, in the Z-direction, between positions of the determinedreference surfaces obtained with respect to the two scanning directions,and to correct, to obtain the measured position, the position of thesurface detected by the detecting unit while the object is scannedrelative to the detecting unit in one of the two scanning directions, inaccordance with a corresponding one of the two scanning directions, withthe calculated offset value and the calculated correction value.

In accordance with another aspect of the present invention, an exposureapparatus is provided for scanning an object in a scanning direction inan X-Y plane, measuring a position of a surface of the object, which isscanning, in a Z direction perpendicular to the X-Y plane, moving theobject, which is scanning, in the Z direction based on the measuredposition, and exposing the object, which is scanning and moving, to apattern. The apparatus includes a measuring apparatus for measuring theposition of the surface of the object. The measuring apparatus includesthose features discussed above.

In accordance with another aspect of the present invention, a method ofmanufacturing a device includes exposing an object to a pattern by useof an exposure apparatus discussed above, developing the exposed object,and processing the developed object to manufacture the device.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a main portion of a projection exposureapparatus of a slit scan type that uses a surface position detectingmethod according to an embodiment of the present invention.

FIG. 2 is a schematic view for explaining a positional relationship ofan exposure slit and measurement points, in the surface positiondetection using a detection optical system.

FIG. 3 is a plan view for explaining an example of the layout of processregions to be exposed, on a wafer, and selection of sample shots forpre-scanning in the present invention.

FIG. 4 is a schematic view for explaining an alternate scan of sampleshots of a process region to be exposed, on a wafer.

FIG. 5 is a schematic view for explaining a positional deviation of themeasurement point, in a process region to be exposed of a wafer.

FIG. 6 is a schematic view for explaining the positional relationship offocus reference points in different scan directions, in accordance witha surface position detecting method of the present invention.

FIG. 7, including FIGS. 7A and 7B, is a flow chart for explaining anexample of offset measurement with the surface position detecting methodof the present invention, as well as a sequence for surface positioncorrective drive during exposure of the shots.

FIG. 8, including FIGS. 8A and 8B, is a flow chart for explaining anexample of a sequence for surface position correcting drive duringexposure, when there is a fault in the wafer flatness in the alternatescan.

FIG. 9 is a flow chart for explaining a semiconductor devicemanufacturing procedure.

FIG. 10 is a flow chart for explaining details of a wafer process in theprocedure shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the attached drawings.

First Embodiment

FIG. 1 is a schematic view of a main portion of a projection exposureapparatus of a slit scan type that uses a surface position detectingmethod according to an embodiment of the present invention.

In FIG. 1, denoted at 1 is a reduction projection lens having an opticalaxis AX. The image plane there is perpendicular to the Z direction.Reticle 2 is held on a reticle stage 3, and a pattern of the reticle 2is projected by a reduction projection lens 1 in a reduced scale,whereby an image is formed on its focal plane. Denoted at 4 is a waferhaving a surface coated with a resist. There are a large number ofprocess regions (shots) to be exposed, arrayed on the wafer, and theseregions have the same pattern structure formed through a precedingexposure process or processes. Denoted at 5 is a wafer stage with an X-Ybar mirror 23 for attracting and fixedly holding the wafer 4. The waferstage 5 comprises an X stage being movable horizontally in the X-axisand Y-axis directions, a leveling stage being movable in the Z-axisdirection and rotatable about the X and Y axes, respectively, and arotational stage being rotatable about the Z axis. The X, Y and Z axesare orthogonal to each other.

Denoted at 10-19 are components of a detection optical system fordetecting a surface position and tilt of the wafer 4. Denoted at 10 is alight source, which comprises a white lamp or an illumination unitarranged to project light of a high-luminance light-emitting diodehaving plural and different peak wavelengths. Denoted at 11 is acollimator lens that receives light from the light source 10 and outputsparallel light having an approximately uniform sectional intensitydistribution. Denoted at 12 is a slit member of a prism-like shape, forproducing slit-like light to be projected on the wafer 4. It comprises apair of prisms being cemented to each other with their slant surfacesopposed to each other. At the cemented surface, there are a plurality ofopenings (for example, six pinholes) defined there by use of a lightblocking film, such as chromium, for example. Denoted at 13 is anoptical system of a bi-telecentric system, and it functions to directsix independent light beams passed through the pinholes of the slitmember 12 toward six measurement points on the wafer 4 surface via amirror 14. Although only two light beams are illustrated in FIG. 1, inthis embodiment, there are light beams of three, being accumulated intoone as seen, in the direction perpendicular to the sheet of the drawing,such that light beams of a total of six are there. Here, with respect tothe lens system 13, the slant surface of the prism where the pinholesare formed, and a plane that contains the wafer 4 surface, are set tosatisfy a Scheinmpflug's condition.

In this embodiment, the incidence angle of each light beam from thelight projecting means 10-14 upon the wafer surface (i.e., the angledefined by a normal to the wafer surface, that is, the optical axis) isΦ=70 degrees or more. On the wafer 4 surface, there are a number ofregions (shots) having the same pattern structure formed through thepreceding exposure process or processes, as shown in FIG. 3. The sixlight beams passed through the lens system 13 are incident on and imagedat respective measurement points CL1, CL2, CL3, CR1, CR2 and CR3 (asshown in FIG. 2), in the pattern region, which measurement points areindependent from each other. Further, in order to assure that these sixmeasurement points are observed on the wafer 4 surface independently ofeach other, the light beams are projected thereon in a direction rotatedby θ (e.g. 22.5 degrees) from the X direction (scan direction) and inthe X-Y plane. This is discussed in Japanese Patent No. 2910327(Japanese Patent Application No. H3-157822) and, with this structure,the spatial disposition of the components is made appropriately, andhigh-precision detection of surface positional information isfacilitated.

Next, structures of detection side components 15-19 for detectingreflection light from the wafer 4 will be explained. The six light beamsfrom the wafer 4 are reflected by the mirror 15, and they are directedto a light receiving optical system 16, which is a bi-telecentricsystem. Inside the light receiving optical system 16, there is a stopper17, which is provided commonly in relation to the six measurementpoints, and it functions to intercept higher-order diffraction light(noise) to be produced by a circuit pattern that is present on the wafer4. The light beams passed through the light receiving optical system 16have their optical axes placed in parallel to each other, and they arere-imaged upon detection surfaces of a photoelectric converting meansgroup 19, respectively, by means of six separate correcting lenses of acorrecting optical system group 18, in the form of light spots havingthe same size. The photoelectric converting means group 19 comprises sixone-dimensional CCD line sensors corresponding to the six measurementpoints. The optical system having elements of 16-18 is tilt-corrected sothat the measurement points on the wafer 4 surface and the detectionsurfaces of the photoelectric converting means group 19 are placed in aconjugate relation with each other. Therefore, any local tilt at eachmeasurement point would not cause a change in the position of a pinholeimage on the detection surface. Thus, it is assured that the position ofthe pinhole image upon the detection surface changes in response to achange in level (height) of a corresponding measurement point in the Zdirection.

Next, a slit-scan type exposure system will be described. As shown inFIG. 1, the reticle 2 is attracted to and held fixed by the reticlestage 3. After this, it is scanningly moved along a plane perpendicularto the optical axis AX of the projection lens 1, and in a direction ofan arrow 3 a (X-axis direction), at a constant speed. Also, as regards adirection orthogonal to the arrow 3 a (i.e., Y-axis direction),corrective drive is made to perform the scan, while continuously keepingthe target coordinate position in that direction. Positional informationregarding the reticle stage 3 with respect to the X and Y directions iscontinuously measured by projecting a plurality of laser beams from areticle stage interferometer system 21 toward an X-Y bar mirror 20 fixedto the reticle stage.

The exposure illumination optical system 6 uses a light source thatproduces pulse light, such as an excimer laser, for example, and itcomprises a beam shaping optical system, an optical integrator, acollimator, a mirror, and so on, not shown in the drawing. Theillumination optical system 6 is made of a material that can efficientlytransmit or reflect pulse light in the deep ultraviolet region. The beamshaping optical system serves to change the sectional shape (includingsize) of the incident beam to a desired shape. The optical integratorfunctions to make uniform the distribution characteristic of light toensure that the reticle 2 is illuminated with a uniform illuminance. Amasking blade (not shown) is provided inside the exposure illuminationoptical system 6, and it functions to set a rectangular illuminationregion corresponding to the chip size. The pattern of the reticle 2 asthus partially illuminated with such an illumination region is projectedthrough the projection lens 1 onto the wafer 4 being coated with aresist.

A main controller 27 serves to control the whole system in accordancewith a scan, so that an image of a portion of the rectangular region ofthe reticle 2, being illuminated, is formed on a predetermined region ofthe wafer 4. As regards the wafer 4, control is performed in relation tothe position in X-Y plane, that is, X-Y coordinates, rotation θ about anaxis parallel to the Z axis, the position in the Z direction, that is,the Z coordinates, and rotations α and β about axes parallel to the Xand Y axes.

Alignment between the reticle 2 and the wafer 4 with respect to the X-Yplane is accomplished by calculating control data on the basis ofpositional data of the reticle stage interferometer 21 and the waferstage interferometer 24, and wafer position data obtainable through analignment microscope (not shown), and by controlling a reticle positioncontrol system 22 and a wafer stage control system 25.

When the reticle stage 3 is to be scanned in the direction of an arrow 3a, the wafer stage 5 is scanned in a direction of an arrow 5 a and at aspeed corrected by an amount corresponding to the reductionmagnification of the projection lens 1. The scan speed of the reticlestage 3 is determined on the basis of the width, in the scan direction,of a masking blade (not shown) of the exposure illumination opticalsystem 6 and the sensitivity of the resist applied to the wafer 4surface, in favor of the throughput.

The alignment in the Z-axis direction with respect to the image of thepattern on the reticle 2, that is, the alignment with reference to theimage plane, is accomplished by controlling a leveling stage in thewafer stage 5 through the wafer position control system 25, on the basisof the result of a calculation made by a surface position detectingsystem 26, which detects level data of the wafer 4. More specifically,from the level data of wafer level measuring spot lights at three pointsdisposed adjacent to the slit with respect to the scan direction, tiltin a direction perpendicular to the scan direction (i.e., tilt about theX axis), as well as the level (height) in the optical axis AX direction,are calculated to determine a correction amount toward the best imageplane position, at the exposure position. Correction is performed on thebasis of this.

In order to detect the position of the process region, to be exposed, ofthe wafer 4 in the Z direction, that is, the position (Z) with respectto the image plane position, as well as a deviation of tilt (α, β), itis very important to measure the wafer 4 surface very accurately. Whenan optical method detection system is used for this purpose, thereoccurs a detection error due to a pattern step difference (topography).However, a pre-scan may be performed prior to the exposure, and acondition with which the focus value can be measured at a highestprecision may be measured. Also, offset control may be made withreference to the height (level) of such a portion of the process regionof the wafer where a highest focus precision is required. By doing so,an error of focus measured values obtained during the scan exposure canbe corrected in real time. This is discussed in Japanese Laid-OpenPatent Application No. H9-045608.

FIG. 7, including FIGS. 7A and 7B, shows an example of a correctionsequence according to the present invention. At step 101, a startcommand is received. At step 102, a wafer is loaded on a wafer stage,and it is attracted to and held by a chuck. Subsequently, formeasurement of the surface shape (plural surface positions) inside aprocess region (shot region) of the wafer to be exposed, with regard tosix sample shot regions, such as depicted by hatching in FIG. 3, forexample, pre-scan measurement is carried out with respect to each shotregion, and the results are stored into a memory. Namely, at step 103,pre-scan measurement in the up direction is carried out and, at step104, pre-scan measurement in the down direction is carried out in thesame region as in the up-direction scan at step 103. The operation atstep 103 and step 104 is carried out repeatedly to all the sample shotregions (six sample shot regions in this example) through step 105. Ineach sample shot region, the pre-scan measurement may be made pluraltimes with respect to each direction.

Subsequently, at step 106, offset correction values to the best imageplane position are calculated as follows. In the apparatus of FIG. 1, inorder to obtain offset values for correcting errors in focus measuredvalues attributable to the difference in surface state at the respectivedetection points, the surface position detection values (surfaceposition data) stored in the memory at step 103 and step 104 are used.While taking, as a reference, the level of such a portion of the processregion of the wafer where a highest focus precision is required,correction values (errors depending on the pattern structure) forcorrecting the surface position data during the scan exposure to thedistance to the best exposure image plane position, are calculated.

FIG. 6 illustrates the relation in the case when, when up- anddown-direction scan measurements are carried out, an up/down directiondifference (measurement error) is produced at the measurement point tobe taken as a reference, due to the influence of jitter.

A portion (i) in FIG. 6 corresponds to the up-direction scan, and aportion (ii) corresponds to the down-direction scan. Referencecharacters A′ and B′ depict focus measurement regions in respective scandirections, and reference characters A and B depict offset referencesurfaces in respective scan directions as determined by the result ofmeasurement corresponding to A′ and B′. A portion (iii) in FIG. 6illustrates a correction method for the up/down direction difference ofthe offset reference surface. For example, if the position in the Z-axisdirection is higher at A than at B, a relation A−B=X (X is up/downdirection difference) is taken, and when the offset control is carriedout while distributing the up/down direction difference of the offsetreference surface at the ratio of a:b (a, b>0), the corrected offsetreference surface can be represented by the following equation:

${A - {\frac{a}{a + b}X}} = {B + {\frac{b}{a + b}{X.}}}$

Through the offset control made to the up/down direction difference ofthe offset reference surface, while distributing the same at anarbitrary proportion, as described above, good focus correction isassured without causing an up/down direction difference in the focuscorrection toward the best image plane position. The offset control maybe done while taking either of the offset reference surfaces A and B asa reference, and no up/down direction difference is produced on thatoccasion.

When the calculation of offset correction value is completed, at step107, during the scan exposure, the surface position detected values atthe detection points for detecting the respective surface positions arecorrected by use of the aforementioned offset correction value, whichmay be

${- \frac{a}{a + b}}X\mspace{14mu}{or}\mspace{14mu}\frac{b}{a + b}X$in accordance with the up/down direction, corresponding to the patternstructure at the detection point. On the basis of the corrected surfaceposition detected values, the process region of the wafer to be exposedis registered with the exposure image plane, and then the exposure iscarried out. Then, chuck attraction is released and the wafer isunlocked (step 108), and thereafter, the procedure is ended (step 109).

The offset correction value obtained through the pre-scan measurement atsteps 103-106 depends on the pattern structure (actual surface steplevel difference in the process region, material of the substrate, andthe like), and the scan speed. For those wafers in the same lot orhaving been processed through the same procedure, the pattern structureand the scan speed can be regarded as being the same. Therefore, offsetcorrection values obtained with regard to at least the first one waferin the lot may be applied to the remaining wafers.

The embodiment described above is merely an example. In the pre-scanmeasurement at steps 103-106, in the plural sample shot regions, asdepicted by hatching in FIG. 3, up-direction scan may be made first toall the sample shot regions and, subsequently, down-direction scan maybe made to all the sample shot regions. The number of the sample shotsis not limited to six, and any number may be used. Further, while inthis embodiment the surface position detection is carried out withrespect to each simple shot, it may be done with respect to every pluralshots.

Second Embodiment

In the above-described method, when the up/down offset correction valuesare compared between shots, and if there is a local eccentricity foundin the up/down correction values, regarding such a point or such a shot,it may be considered that there is an influence of a defect in the waferflatness due to a process factor or a chuck factor. In such a case, thedata related to such a point or shot may be excluded from calculation ofthe offset correction value, and this is effective to increase theprecision of the offset correction value.

Such an embodiment will be described with reference to the flow chart ofFIG. 8. In FIG. 8, which includes FIGS. 8A and 8B, a start command isreceived at step 201. At step 202, a wafer is loaded on a wafer stage,and it is attracted to and held by a chuck. Subsequently, formeasurement of the surface shape (plural surface positions) inside achip region or process region (shot region) of the wafer to be exposed,with regard to plural sample shot regions, such as depicted by hatchingin FIG. 3, for example, pre-scan measurement is carried out with respectto each shot region, and the results are stored into a memory. Namely,at step 203, pre-scan measurement in the up direction is carried outand, at step 204, pre-scan measurement in the down direction is carriedout in the same region as in the up-direction scan at step 203. Theoperation at step 203 and step 204 is carried out repeatedly to all thesample shot regions (six sample shot regions, in this example).

Thereafter, at step 205, a discrimination is made as to whether the shotis the last sample shot or not. If it is the last sample shot (YES), atstep 206 the up/down direction difference is calculated on the basis ofthe surface position detected values (surface position data) as measuredby the up/down scans and memorized into the memory. Also, if, as aresult of a discrimination at step 205, the shot is not the last sampleshot, the sequence goes back to step 203.

At step 207, when any of the up/down direction difference is less than apredetermined amount (NO), the sequence goes to step 208, at which theoffset correction values toward the best image plane position arecalculated in accordance with the calculation method in the firstembodiment. Here, the predetermined amount may be determined on thebasis of an average value obtainable from all the sample shots and/orreticle design, for example.

If, at step 207, any of the up/down direction differences is larger thanthe predetermined amount (YES), it is concluded that this is because ofa defect, or the like, of the wafer flatness due to process factor orchuck factor, and the sequence goes to step 211. At step 211, offsetcorrection values toward the optimum image plane position are calculatedin accordance with the calculation method of the first embodiment, andon the basis of the up/down scan measurement data with the dataconcerning the error point in question being excluded. When thecorrection value calculation is completed at step 208 or step 211,exposure is carried out at step 209, while at step 209, during the scanexposure, the surface position detected values at the detection pointsfor the surface position detection are corrected by the correctionvalues corresponding to the pattern structure, for example, at thedetection point, and additionally, the process region to be exposed isregistered with the exposure image plane on the basis of the thuscorrected surface position detected values. After this, at step 216, thechuck attraction is released, and the wafer is unloaded. Following that,the procedure is finished in step 212.

In accordance with the first and second embodiments describedhereinbefore, even if there is a positional deviation (jitter) at themeasurement point as produced in accordance with the scan direction,since a scan direction difference of a measured value is taken intoaccount during the calculation process of the offset amounts, thesurface position measured values influenced by the surfaceirregularities of the process region (shot) can be well corrected athigh precision.

Thus, in slit-scan type exposure apparatuses, by performing offsetcorrection to the surface position measured values as described, eachprocess region (shot) of the wafer can be exactly positioned within theDOF (depth of focus) of the reduction projection lens 1. Therefore, goodpattern transfer is assured, and large-scale integrated circuits can beproduced stably.

As regards the point or shot with respect to which the up/down directiondifference of the surface position detected values is larger than apredetermined amount, since it may be a result of influence of a defect,or the like, of the wafer flatness due to a process factor, for example,the detected value in question may be excluded from the calculation ofthe offset correction value. This effectively improves the precision ofthe offset correction value.

Embodiment of Device Manufacturing Method

Next, an embodiment of a device manufacturing method, which uses anexposure apparatus described above, for the production of microdevices,such as semiconductor devices, will be explained.

FIG. 9 is a flow chart for explaining the procedure of manufacturingvarious microdevices, such as semiconductor chips (e.g., ICs or LSIs),liquid crystal panels, CCDs, thin film magnetic heads or micro-machines,for example. Step 1 is a design process for designing a circuit of asemiconductor device. Step 2 is a process for making a mask on the basisof the circuit pattern design. Step 3 is a process for preparing a waferby using a material such as silicon. Step 4 is a wafer process, which iscalled a pre-process, wherein, by using the thus prepared mask andwafer, a circuit is formed on the wafer in practice, in accordance withlithography. Step 5, subsequent to this, is an assembling step, which iscalled a post-process, wherein the wafer having been processed at step 4is formed into semiconductor chips. This step includes an assembling(dicing and bonding) process and a packaging (chip sealing) process.Step 6 is an inspection step, wherein an operation check, a durabilitycheck and so on, for the semiconductor devices produced by step 5, arecarried out. With these processes, semiconductor devices are produced,and they are shipped (step 7).

FIG. 10 is a flow chart for explaining details of the wafer process atstep 4 in FIG. 9. Step 11 is an oxidation process for oxidizing thesurface of a wafer. Step 12 is a CVD process for forming an insulatingfilm on the wafer surface. Step 13 is an electrode forming process forforming electrodes upon the wafer by vapor deposition. Step 14 is an ionimplanting process for implanting ions to the wafer. Step 15 is a resistprocess for applying a resist (photosensitive material) to the wafer.Step 16 is an exposure process for printing, by exposure, the circuitpattern of the mask on the wafer through the exposure apparatusdescribed above. Step 17 is a developing process for developing theexposed wafer. Step 18 is an etching process for removing portions otherthan the developed resist image. Step 19 is a resist separation processfor separating the resist material remaining on the wafer after beingsubjected to the etching process. By repeating these processes, circuitpatterns are superposedly formed on the wafer.

With these processes, high density microdevices can be manufactured.

In accordance with the present invention, as described above, improvedsurface position detecting technology, by which a position of a surfaceof an object can be detected very precisely, is provided.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

1. A method comprising: a detecting step of pre-scanning an objectrelative to a detection unit in two scanning directions, in an X-Yplane, opposite to each other, the detection unit being configured todetect a position of the surface of the object in a Z directionperpendicular to the X-Y plane, and detecting, using the detection unit,with respect to each of the two scanning directions, a position of thesurface in the Z-direction for each of the same detection points on thesurface; a calculating step of determining, with respect to each of thetwo scanning directions, a reference surface based on the detectedpositions of the surface obtained in said detecting step, calculating anoffset value, which is a difference between the detected position and aposition of the reference surface in the Z-direction for each of thesame detection points with respect to each of the two scanningdirections, calculating a correction value for correcting the calculatedoffset value in accordance with a corresponding one of the two scanningdirections based on a difference, in the Z-direction, between positionsof the determined reference surfaces obtained with respect to the twoscanning directions; a correcting step of correcting, to obtain themeasured position, the position of the surface detected by the detectionunit while the object is scanned relative to the detection unit in oneof the two scanning directions, in accordance with a corresponding oneof the two scanning directions, with the calculated offset value and thecalculated correction value obtained in said calculating step; ascanning step of scanning the object in one of the two scanningdirections; a moving step of moving the scanning object in the Zdirection based on the corrected position obtained in accordance with acorresponding one of the two scanning directions in said correctingstep; and an exposing step of exposing the scanning, moving object to apattern.
 2. A method according to claim 1, wherein the object is asemiconductor wafer.
 3. A method according to claim 1, wherein saiddetecting step detects the position of the surface with respect to eachof a plurality of sample shot regions on the surface.
 4. A methodaccording to claim 3, wherein said calculating step chooses data of theposition of the surface to be used for calculation of the offset valuebased on a difference between the positions of the surface detected forthe same detection point with respect to the two scanning directions insaid detecting step.
 5. A method according to claim 1, wherein saidcalculating step weighted-averages the determined reference surfacesobtained with respect to the two scanning directions and calculates thecorrection value based on the weighted-averaged surface.
 6. A measuringapparatus for measuring a position of a surface of an object while theobject is scanned in a scanning direction in an X-Y plane, saidapparatus comprising: a detecting unit configured to detect the positionof the surface of the object in a Z direction perpendicular to the X-Yplane; a stage configured to scan the object relative to said detectingunit in the scanning direction; and a controller configured to causesaid stage to pre-scan the object relative to said detecting unit in twoscanning directions, in the X-Y plane, opposite to each other, todetect, using said detecting unit, with respect to each of the twoscanning directions, a position of the surface in the Z-direction foreach of the same detection points on the surface, to determine, withrespect to each of the two scanning directions, a reference surfacebased on the detected positions of the surface, to calculate an offsetvalue, which is a difference between the detected position and aposition of the reference surface in the Z-direction for each of thesame detection points with respect to each of the two scanningdirections, to calculate a correction value for correcting thecalculated offset value in accordance with a corresponding one of thetwo scanning directions based on a difference, in the Z-direction,between positions of the determined reference surfaces obtained withrespect to the two scanning directions, and to correct, to obtain themeasured position, the position of the surface detected by saiddetecting unit while the object is scanned relative to said detectingunit in one of the two scanning directions, in accordance with acorresponding one of the two scanning directions, with the calculatedoffset value and the calculated correction value.
 7. A measuringapparatus according to claim 6, wherein the object is a semiconductorwafer.
 8. A measuring apparatus according to claim 6, wherein saidcontroller is configured to detect, using said detecting unit, theposition of the surface with respect to each of a plurality of sampleshot regions on the surface.
 9. A measuring apparatus according to claim8, wherein said controller is configured to choose data of the positionof the surface to be used for calculation of the offset value, based ona difference between the positions of the surface detected for the samedetection point with respect to the two scanning directions.
 10. Ameasuring apparatus according to claim 6, wherein said controller isconfigured to weighted-average the determined reference surfacesobtained with respect to the two scanning directions, and to calculatethe correction value based on the weighted-average surface.
 11. Anexposure apparatus for scanning an object in a scanning direction in anY plane, measuring a position of a surface of the object, which isscanning, in a Z direction perpendicular to the X-Y plane, moving theobject, which is scanning, in the Z direction based on the measuredposition, and exposing the object, which is scanning and moving, to apattern, said apparatus comprising: a measuring apparatus for measuringthe position of the surface of the object, said measuring apparatuscomprising: (i) a detecting unit configured to detect the position ofthe surface of the object in a Z direction perpendicular to the X-Yplane; (ii) a stage configured to scan the object relative to saiddetecting unit in the scanning direction; and (iii) a controllerconfigured to cause said stage to pre-scan the object relative to saiddetecting unit in two scanning directions, in the X-Y plane, opposite toeach other, to detect, using said detecting unit, with respect to eachof the two scanning directions, a position of the surface in theZ-direction for each of the same detection points on the surface, todetermine, with respect to each of the two scanning directions, areference surface based on the detected positions of the surface, tocalculate an offset value, which is a difference between the detectedposition and a position of the reference surface in the Z-direction foreach of the same detection points with respect to each of the twoscanning directions, to calculate a correction value for correcting thecalculated offset value in accordance with a corresponding one of thetwo scanning directions based on a difference, in the Z-direction,between positions of the determined reference surfaces obtained withrespect to the two scanning directions, and to correct, to obtain themeasured position, the position of the surface detected by saiddetecting unit while the object is scanned relative to said detectingunit in one of the two scanning directions, in accordance with acorresponding one of the two scanning directions, with the calculatedoffset value and the calculated correction value.
 12. A method ofmanufacturing a device, said method comprising: exposing an object to apattern by use of an exposure apparatus defined in claim 11; developingthe exposed object; and processing the developed object to manufacturethe device.